The PEER (Publishing and the Ecology of European Research) project will examine "the effects of the large-scale, systematic depositing of authors' final peer-reviewed manuscripts . . . on reader access, author visibility, and journal viability, as well as on the broader ecology of European research." The project will conclude in 2011.

Here's an excerpt from the press release:

The aim of PEER is to build a substantial body of evidence, by developing an 'observatory' to monitor the effects of systematic archiving over time. Participating publishers will collectively contribute 300 journals to the project and supporting research studies will address issues such as:

How large-scale archiving will affect journal viability

Whether it increases access

How it will affect the broader ecology of European research

Which factors influence the readiness to deposit in institutional and disciplinary repositories and what the associated costs might be

Models to illustrate how traditional publishing systems can coexist with self-archiving

The International Association of Scientific, Technical and Medical Publishers (STM), the European Science Foundation, Gottingen State and University Library, the Max Planck Society and INRIA will collaborate on PEER, supported by the SURF Foundation and University of Bielefeld, which will contribute the expertise of the EU-funded DRIVER project.